In one type of filter press, filter cloths are held between a horizontally arranged series of plates. The plates have projecting support arms which are slideable on spaced, parallel support rails. Periodically the plates and filter cloths must be separated for cake removal and cleaning. Separating all of the plates for access to all at the same time is readily provided for but requires that the rails and the machine be of considerable length. Shifting only one or several plates in successive order allows the machine instead to be shorter overall, but requires a dependable mechanism for that purpose.
Most such mechanisms of the prior art are of considerable complexity. The present invention is an improvement over one of the less complex prior art mechanisms which will be described in connection with a filter press of improved design and which includes filter plates and intermediate diaphragm plates. Typically, such a press may include up to one hundred and fifty such plates which require shifting.
The frame of the typical, horizontal filter press includes two, parallel support rails which connect the fixed head at one end of the machine and a hydraulic ram at the other end. The moveable head is moved by the ram toward or away from the fixed head as required and is supported for such movement by and between the two rails. The plates are slidably supported on and between the rails and are disposed between the two heads. Filter cloths are suspended between each two adjacent plates. In the filter press here being described, the first plate is disposed adjacent to the moveable head and the first, third, etc. including the last plate are filter plates. All of said filter plates except possibly the plate which is adjacent to the fixed head also include oppositely projecting pins, the pins of each plate projecting respectively from the two vertical sides of the plate and over the two rails. The other, that is, the second, fourth, etc. including the second-last plate are diaphragm plates. They are connected respectively to the first, third, etc. filter plates by flexible cables of fixed identical lengths or other suitable means as will appear.
The prior art shifting mechanism includes an endless chain alongside each rail and operating over a drive sprocket at the ram end and a driven sprocket at the fixed head end of the machine. The two drive sprockets are mounted on a shaft extending across the ram end of the machine and a shaft drive means causes the upper runs of the two chains to move toward said ram end of the machine. The critical elements of the mechanism include a pair of pawls which are pivotally connected respectively to two corresponding links of said chains. Each pawl extends forwardly of such link having reference to its direction of movement as effected by the drive means and extends upwardly of the upper run and downwardly of the lower run. That is, as to the lower run, the pawls hang from their chains.
A track between the sprockets at each side of the machine slidably supports the upper run of the respective chain a precise distance immediately and directly below the series of pins projecting from the plates such that in their upper engaging position, the two pawls of the two chains simultaneously engage respectively the projecting pins extending from the filter plate which is to be moved on the rails a distance toward the movable head. In their lower passing position, the two pawls pass under the pins of all the other filter plates so as not to move any which have already been or are subsequently to be shifted. Each pawl is biased upwardly by counterweights for that purpose and is provided with a forwardly projecting cam which engages or does not engage the pins to pivot the pawl downwardly or allow it to pivot upwardly as required. The cam engages and slides against the pins or support arms and is moved downwardly by the forward movement of the pawl such that the cam pivots the pawl downwardly. The proximal portion of the cam is straight and is extended to slide against the undersides of the pins and hold the pawl in its passing position.
The required form and length of the cam is determined by the spacing of the pins of the plates which are in the open position relative to the spacing of those which are in the closed position. This may be further and best explained by describing the opening and the closing cycles of the press.
For filtering, all the plates are under compression and are, of course, equally spaced. For cleaning, the feed is stopped and the movable head is retracted toward one end of the machine. The two chains are then driven to move the pawls beneath the projecting pins of the filter plates. All the pins are relatively close together so that they in cooperation with the cams hold the pawls in their passing positions until having passed the pins of the first filter plate to be moved. When the cams have passed the pins referred to and there being then no pins holding the pawls in their passing position, the pawls are biased upwardly to engage the pins of the first plate. Thereupon, the movement of the first plate away from the second is initiated and proceeds to the extent allowed by the pair of cables or other means connecting the two plates so as to maintain a limited spacing therebetween. The first and second plates then move together until the nose of each cam reaches a pin carried by the movable head.
As the two cams are depressed by the pins of the moveable head, the pawls are pivoted to their lower passing positions and the pawls disengage the pins of the first plate. The first plate is now again adjacent to the movable head and the first, second and third plates are suitably spaced for cake removal and the first cleaning cycle by other apparatus which need not be described here.
During the cleaning cycle the chains continue to operate so that two pawls are ready to engage the next plate. After the first cleaning cycle, the pair of pawls next engage the pins of the third plate. The movement of that plate then proceeds until it is spaced from the fourth plate and their connecting cables are then operative such that both plates are moved toward the ram end of the machine. At about the same time, the third plate engages the second plate which it also moves toward the first plate. When and as the two cams reach and are depressed by the pins of the first plate, the pawls are disengaged from the pins of the third plate so that the pawls pass under the latter pins and the pins of the movable head. Such disengagement now leaves the third, fourth and fifth plates suitably spaced for the cleaning cycle which proceeds while pawls are positioned to enggae the fifth plate of the machine. In the next sequence, the third, fourth and fifth plates are reclosed and the fifth, sixth and seventh plates are suitably spaced and so on. After the cleaning of the last three plates, the drive means is stopped. For resumption of the filtering operation, the ram pushes the movable head and the plates are all pushed together or regrouped.
Each two pawls are carried by the chains in precisely parallel paths. However, for example, if either pawl malfunctions, the plate which is being shifted by the other pawl will be skewed and require considerable repair.
It is the object of the present invention to provide pawls which operate smoothly and reliably and which readily engage and disengage the support arms of the plates.
It is another object to provide track means for the pawls so that they are well guided and retracted as they move around the sprockets.
It is another object to increase the life expectancy of such apparatus and to reduce operating noise and wear of the operating parts.
It is another object to provide an improved support of the return run of the chain so that although some slack in the chain may be allowed to develop, the engagement of the chain and drive sprocket is fully maintained in any case so that all of the foregoing advantages are realized.